1. Field of the Invention
The present invention relates to an input system, and more particularly, to an input system which may implement a stylus pen without a battery, detect both touch by fingers and touch by the stylus pen, and increase sensitivity to writing pressure.
2. Discussion of the Related Art
As the information age has arrived, the field of displays visually expressing electrical information signals has rapidly developed, and in order to satisfy such a trend, various flat display devices having excellent performance, such as thin thickness, light weight and low power consumption, have been researched and rapidly replaced conventional cathode ray tubes (CRTs).
Flat display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), electro luminescence displays (ELDs), etc. These display devices essentially include a flat display panel displaying a picture in common, and the flat display panel is configured such that a pair of transparent insulating substrates is bonded under the condition that a light emitting material layer or an optically anisotropic material layer is interposed between the substrates.
In such a display device, requirements to add a touch panel recognizing a touched region through a human hand or a separate input unit and transmitting corresponding separate information are increased. Recently, such a touch panel is attached to the external surface of the display device.
Touch panels are divided into a resistive type, a capacitive type, an infrared sensing type, etc., according to touch sensing methods, and the capacitive type is in the spotlight in consideration of ease in the manufacturing method and sensing force.
Recently, a human interface device (HID), such as a smart phone or a smart book, as a mobile device increasingly uses a stylus pen which implements writing and drawing as well as touch input through fingers, as an input unit. Input through the stylus pen executes more precise input as compared to input through fingers, and supports functions, such as precise picture drawing and character writing.
Hereinafter, with reference to the accompanying drawings, a general capacitive-type touchscreen will be described.
FIG. 1 is a circuit diagram illustrating a general capacitive-type touch detection circuit, and FIG. 2 is a graph illustrating voltage output according to time divided by whether or not fingers touch the circuit using the circuit diagram of FIG. 1.
As exemplarily shown in FIG. 1, the general capacitive-type touch detection circuit includes first electrodes Tx and second electrodes Rx which intersect each other, an amplifier 5 provided with a negative (−) input terminal receiving output of the second electrode Rx and a positive (+) input terminal receiving reference voltage Vref, and a capacitor Cs formed between an output terminal and the negative (−) input terminal of the amplifier 5.
Here, input voltage Vin is applied through a pad provided at one end of the first electrode Tx, and output voltage Vout output through the amplifier 5 is sensed through a pad provided at one end of the second electrode Rx.
In general, a touch drive signal of square waves of about 2˜3 μs is applied to the first electrode Tx as the input voltage Vin. Here, a voltage value in proportion to mutual capacitance Cm between the first and second electrodes Tx and Rx is sensed as the output voltage Vout.
As exemplarily shown in FIG. 2, when the square waves are applied as the input voltage Vin, the output voltage Vout increases (if the circuit is not touched by fingers) as time goes by, and, if the circuit is touched by fingers, the fingers contact the electrodes, the mutual capacitance Cm decreases and thus the increment of the output voltage Vout decreases. Then, such decrement is detected at the respective intersections of Tx channels and Rx channels, and coordinates of a region of the circuit touched by the fingers are extracted from these data.
However, when the touch detection circuit is touched by a stylus pen rather than fingers, a contact area of the tip of the stylus pen with the surface of a sensor panel is relatively small, mutual capacitance variation ΔCm between the electrodes is small, and thus sensing of the mutual capacitance variation ΔCm when the touch detection circuit is touched by the stylus pen may be difficult. Thereby, accuracy in extraction of coordinates may be lowered.
Further, if the tip of the stylus pen is smaller than the electrodes provided on the sensor panel for sensing, distortion of coordinates may occur according to presence or absence of the electrodes, and this may directly influence sensitivity.
Further, in case of finger touch and stylus pen touch, when the same touch detection circuit is used, touch by a palm contacting the electrodes and touch by the stylus pen during input by the stylus pen may not be discriminated from one another. That is, it may be difficult for the detection circuit of FIG. 1 to perform a palm rejection function when the detection circuit is touched by the stylus pen.
Further, a method of detecting stylus pen touch in a driving type differing from the driving type of finger touch, for example, an electromagnetic driving type, is proposed. However, in this case, a panel which may execute detection through electromagnetic driving needs to be separately provided in addition to capacitive-type electrodes, and thus the number of components is increased and the number of processes is increased.
The above-described general capacitive-type touchscreen has problems, as follows.
First, since a contact area of the tip of the stylus pen with the sensor panel surface is relatively small, mutual capacitance variation ΔCm between the electrodes is small, and thus sensing of the mutual capacitance variation ΔCm when the touch detection circuit is touched by the stylus pen may be difficult. Thereby, accuracy in extraction of coordinates may be lowered.
Second, if the tip of the stylus pen is smaller than the electrodes provided on the sensor panel for sensing, distortion of coordinates may occur according to presence or absence of the electrodes, and this may directly influence sensitivity.
Third, in case of finger touch and stylus pen touch, when the same touch detection circuit is used, touch by a palm contacting the electrodes and touch by the stylus pen during input by the stylus pen may not be discriminated from one another. That is, it may be difficult for the capacitive-type touchscreen to perform a palm rejection function when the touchscreen is touched by the stylus pen.
Fourth, a method of detecting stylus pen touch in a driving type differing from the driving type of finger touch, for example, an electromagnetic driving type, is proposed. However, in this case, a panel which may execute detection through electromagnetic driving, in addition to capacitive-type electrodes, needs to be separately provided and thus the number of components is increased and the number of processes is increased.